Preheat your oven to 350°F (175°C) and lightly grease a standard 6-cup silicone muffin tin with a touch of olive oil or cooking spray.
In a medium skillet over medium heat, add the olive oil and sauté the ground turkey and finely diced red onion until the turkey is fully browned and the onions are translucent.
Add the chopped fresh spinach to the skillet and stir for 1-2 minutes until just wilted, then remove the pan from heat to cool slightly.
In a separate mixing bowl, whisk together the egg whites, sea salt, black pepper, and garlic powder until well combined and slightly frothy.
Distribute the turkey and spinach mixture evenly among the 6 muffin cups, pressing down slightly to ensure they are packed.
Pour the egg white mixture over the turkey and spinach until each cup is nearly full, allowing the liquid to seep into the gaps.
Sprinkle the crumbled feta cheese over the top of each egg bite for a savory, tangy finish.
Bake for 20 to 25 minutes, or until the egg whites are firm to the touch and the edges are slightly golden.
Allow the bites to cool in the tin for 5 minutes before gently popping them out to serve warm.